This project involves a study of the mechanism of selective antibody absorption by the human placenta and guinea pig yolk sac placenta. The methods used for study include localization of antibodies in the tissue by immunocytochemical techniques, or the absorption, in vitro, of enzyme-conjugated antibodies. The localization of the molecules and their pathways of transport are examined by light and electron microscopy. A comparison will be made between the localization of the various classes of immunoglobulins in the placenta. By similar methods, the localization of transferrin on the surface of the placenta is being examined. The fine structure and protein absorptive activity of the amnion will be examined utilizing electron-dense tracer proteins. Studies on the comparative fine structure of the mammalian placenta will be carried ou on six species of cricetid rodents which heretofore have not been examined. BIBLIOGRAPHIC REFERENCES: King, B.F. 1975 The fine structural localization of immunoglobulin G in the human placenta. Anat. Rec., 181: 394. King, B.F. and D.N. Menton 1975 Scanning electron microscopy of human placental villi from early and late in gestation. Am. J. Obstet. Gynecol., 122: 824-828.